Injection device

ABSTRACT

Injection devices are known for the self administration of medicament by patients, in which the medicament is typically contained within a cartridge located within the injection device. It is a problem that injection devices should be small enough to fit into a jacket pocket or a hand bag without difficulty. Also, the injection device must be of a size that enables a piston or the like used to drive the cartridge bung within the cartridge to be moved both to a maximum dispense position within the cartridge and to be fully withdrawn from the cartridge to allow for replacement of the cartridge. A drive mechanism for an injection device is disclosed in which a piston  42  comprises a first piston part  44  guided for linear movement to selectively drive a bung  18  and a second piston part  46  connected for pivoting movement with respect to the first piston part  44.

The present invention relates to improvements in an injection device,and in particular to improvements in a portable injection device fordispensing controlled quantities of a medicament.

Injection devices are known for the self administration of medicament bypatients. For example, those suffering from diabetes may require regularinjections of insulin. Injection devices allow the patient to select adose and to administer that dose. It is known to automate this processso that a user need only press a button and the injection device willdispense a selected dose of medicament. This relieves the patient of thetask of controlling the amount dispensed while manually expelling themedicament from the injection device. This is a particular problem forthe elderly, the infirm, those suffering from vision difficulties andothers suffering from diabetes related problems which impair theirfaculties.

The medicament is typically contained within a cartridge located withinthe injection device. The cartridge has a bung or piston at one endwhich is driven towards a second end of the cartridge to expel themedicament from the injection device. It is a problem that injectiondevices should be small enough to fit into a jacket pocket or a hand bagwithout difficulty. At the same time, the injection device must be of asize that enables a piston or the like used to drive the cartridge bungwithin the cartridge to be moved both to a maximum dispense positionwithin the cartridge and to be fully withdrawn from the cartridge toallow for replacement of the cartridge.

It is an advantage of the present invention that it seeks to provide asolution to these conflicting requirements.

According to a first aspect of the present invention, a drive mechanismfor an injection device in which a piston is successively moved inrelation to a first end of a medicament cartridge containing amedicament selectively to drive a bung closing a first end of themedicament cartridge into the medicament cartridge to expel medicamentthrough a delivery member located at a second end of the medicamentcartridge, is characterised in that the piston comprises a first pistonpart guided for linear movement to selectively drive the bung and asecond piston part connected for pivoting movement with respect to thefirst piston part.

Preferably, the drive mechanism further comprises a transmission meansbetween a dial dose mechanism and the piston.

Preferably, the transmission means comprises a dose setting mechanismconnected to drive the piston through a dispense gear. More preferably,the dose setting mechanism comprises a spline connecting a dosing shaftto the dial dose mechanism, the dosing shaft having a first abutmentsurface at a second end. Even more preferably, the button has a stopsurface for abutment with the abutment surface of the dosage shaft.

According to a second aspect of the present invention, an injectiondevice incorporates a drive mechanism according to the first aspect ofthe invention.

The invention will now be described, by way of example only, withreference to the accompanying drawings in which:

FIG. 1 shows in side section an injection device having a deliverydevice according to the present invention;

FIG. 2 shows a similar view to FIG. 1 with the injection device in readyposition;

FIG. 3 shows a view similar to FIG. 2 after dialling of a requireddosage;

FIG. 4 shows a view similar to FIG. 3 after delivery of the requireddosage; and

FIG. 5 shows a side section of a mechanism for use with the injectiondevice of FIGS. 1 to 4.

Like reference numerals will be used to refer to like parts of theinjection device.

Referring first to FIG. 1, there may be seen an injection device 2incorporating a drive mechanism 4 in accordance with the presentinvention.

The injection device 2 comprises a main housing 6, the drive mechanism 4including a dial dose mechanism 10, and a button 12. A needle unit 14including a delivery member in the form a hollow needle is secured to afirst end of the main housing 6. A medicament cartridge 16 having afirst end and a second end may be stored in the main housing 6. When theneedle unit 14 is in place, the needle unit pierces a flexible membraneat the first end of the medicament cartridge 16. A displaceable bung 18is located at the second end of the medicament cartridge 16. A cover(not shown) may be provided over the first end of the main housing 6 toprotect the needle unit from damage and a user from inadvertent prickingby the needle.

The button 12 is preferably in the form of a cup or cap adapted forslidable movement within the main housing as shown in the illustratedembodiment. The main housing 6 and the button 12 are preferably providedwith a catch (not shown) releasably to retain the button 12 in a closedor ‘off’ position. The button 12 is provided with a stop member 20extending from an inner side of the button 12.

The dial dose mechanism 10 is located towards the first end of the mainhousing 6. The dial dose mechanism 10 is used by a user to select adosage of medicament to be dispensed from the injection device in amanner to be described. The dose dial mechanism 10 is located adjacent adose setting mechanism The dose dial mechanism 10 is connected to thedose setting mechanism by way of a gear arrangement 22.

The dose setting mechanism comprises a dosing shaft 24 having a radiallyextending flange 26 about a portion intermediate between a first end ofthe dosing shaft 24 and a second end of the dosing shaft 24. Theradially extending flange 26 has a first surface which in use may abutan abutment surface provided within the main housing 6. A spline 30 isprovided about the first end of the dosing shaft 24 whereby the dosingshaft 24 is connected to the gear arrangement 22. The second end of thedosing shaft 24 is provided with a threaded portion 32 along at leastapart thereof The second end of the dosing shaft 24 is further providedwith an abutment surface 34 for abutment with the stop member 20 on thebutton 12.

The drive mechanism comprises a dispense gear 40 located for rotationwithin the main housing 6, a piston 42 having a first piston part 44 anda second piston part 46 and guide means 48 located within the mainhousing 6. The guide means 48 comprises a fist rectilinear portion 50and a curved portion 52. Each of the first piston part 44 and the secondpiston part 46 are provided with a toothed or threaded portion 54 alongat least one side thereof. The first piston part 44 and the secondpiston part 46 are pivotally connected to one another about a pivotpoint 56.

In FIG. 1, the injection device 2 is shown with a full medicamentcartridge 16 with the drive mechanism a fully retracted position and thebutton 12 fully depressed. The dispense gear 40 engages both thethreaded portion 32 of the dosing shaft 24 and the threaded or toothedregion 54 of the first piston part 44.

To operate the injection device 2 a user releases the button 12 from theretained or ‘off’ position such that the button 12 slides outwardly fromwithin the main housing 6 (FIG. 2).

To set a required dosage a user sets a dose using the dose dialmechanism 10. This causes the gear arrangement 22 to precess the dosingshaft 24 with respect to the spline 30 thereby moving the abutmentsurface 34 of the dosing shaft 24 towards the stop member 20 on thebutton 12 (FIG. 3).

The user can now operate the injection device to deliver the dosage setby depressing the button 12. As the button 12 is displaced within themain housing 6, the stop member 20 on the inside of the button 12 comesinto contact with the abutment surface 34 of the dosing shaft 24.

Further displacement causes the dosing shaft 24 to be driven towards thefirst end of the injection device 2. This further displacement causesthe dispense gear 40 to be rotated due to the travel of the threadedportion 42 of the dosing shaft 24. The rotation of the dispense gear 40causes the toothed or threaded portion 54 of the first piston part 44 tobe driven towards the displaceable bung 18. This in turn causes rotationof the second piston part 46 about the linearly displaced pivot point 56as the first piston part 44 is driven into the rectilinear portion 50 ofthe guide means 48. Concurrently, the second piston part 46 is guided bythe curved portion 52 of the guide means 48 towards and into therectilinear portion 50 of the guide means by the action of the firstpiston part 44. It will be seen that a swinging movement of a free endof the second piston part 46 occurs within the fully retracted positionof the button 12 (FIG. 4). The further displacement of the dosing shaft24 continues until the button 12 has been fully depressed.

On the next use of the injection device 2, a new dose is set, precessingthe dosing shaft 24 further prior to depression of the button 12. As theprocess is repeated the first piston part 44 is driven further into therectilinear portion 50 of the guide means, such that the first pistonpart 44 passes beyond the dispense gear 40. At this point, the dispensegear 40 engages with the toothed or threaded region 54 of the secondpiston part 46 to drive the second piston part 46. The first piston part44 is then driven towards the displaceable bung 18 under the action ofthe second piston part 46.

This process is repeated until replacement of the medicament cartridge16 is required (FIG. 5). The first piston part 44 and the second pistonpart 46 can then be withdrawn from the medicament cartridge 16 under theaction of the dispense gear 40 to allow subsequent replacement of themedicament cartridge 16.

The relative an arrangement of the drive mechanism and the medicamentcartridge means that the main housing provides a relatively large flatface where a relatively large dose display, such as a liquid crystaldisplay may be located. This in turn enables the dose display to userelatively large figures or other characters. This is an advantage forthose with impaired vision.

1. A drive mechanism for an injection device, comprising: a piston thatis successively moved in relation to a first end of a medicamentcartridge containing a medicament selectively to drive a bung closing afirst end of the medicament cartridge into the medicament cartridge toexpel medicament through a delivery member located at a second end ofthe medicament cartridge, the piston further comprising: a first pistonpart guided for linear movement to selectively drive the bung; and asecond piston part connected for pivoting movement with respect to thefirst piston part, wherein the piston is driven through a dispense gearby a dosing shaft.
 2. A drive mechanism according to claim 1, furthercomprising a transmission mechanism between a dial dose mechanism andthe piston.
 3. An injection device incorporating a drive mechanismaccording to claim
 2. 4. A drive mechanism according to claim 2, whereinthe transmission mechanism comprises a dose setting mechanism connectedto drive the piston through the dispense gear.
 5. An injection deviceincorporating a drive mechanism according to claim
 4. 6. A drivemechanism according to claim 4, wherein the dose setting mechanismcomprises a spline connecting the dosing shaft to the dial dosemechanism, the dosing shaft having an abutment surface at one end.
 7. Aninjection device incorporating a drive mechanism according to claim 6.8. A drive mechanism according to claim 6, wherein a button has a stopsurface for abutment with the abutment surface of the dosing shaft. 9.An injection device incorporating a drive mechanism according to claim8.
 10. An injection device incorporating a drive mechanism according toclaim
 1. 11. An injection device according to claim 10, furthercomprising a drive means selectively to drive the bung having a buttondisplaceably housed in the injection device.